Coalition forces have begun a massive air campaign against Iraq, pounding military targets in Baghdad and other Iraqi cities after the apparent failure of efforts to force Saddam Hussein's government to relinquish power without a fight.

Top Pentagon officials say the long-awaited air campaign is underway, targeting hundreds of selected leadership and military sites in Baghdad and various other cities, mainly in the north.

Large explosions were seen rocking the Iraqi capitol, sending enormous fireballs and plumes of thick smoke rising high over the city.

Among the targets hit was a presidential palace.

The U.S. military had promised it would launch a bombing campaign unprecedented in the history of warfare that would produce "shock and awe." Hundreds of aircraft and cruise missiles are involved.

Meanwhile, U.S. and British soldiers on land have pushed about 160 kilometers into Iraq, capturing key territory in the southern and western parts of the country.

U.S. Defense Secretary Donald Rumsfeld said the government of Iraq is beginning to lose control of the country. "The confusion of Iraqi officials is growing. Their ability to see what is happening on the battlefield, to communicate with their forces and to control their country is slipping away," he said. "They are beginning to realize, I suspect, that the regime is history."

Coalition soldiers are encountering both hostile fire and surrendering Iraqi troops in their race across the desert toward Baghdad and Basra.

U.S. defense officials say American forces have seized two airfields in Western Iraq without significant resistance. Officials say the airfields could be sites for storing Iraqi Scud missiles or weapons of mass destruction. Coalition forces have seized the port of Umm Qasr and British soldiers have captured the strategic Faw peninsula on the Persian Gulf.

U.S. General Richard Myers, the Chairman of the Joint Chiefs of Staff, said so far, the war is going virtually according to plan. "Clearly we are moving towards our objectives," said General Myers, "but we must not get too comfortable. We are basically on our plan and moving towards Baghdad, but there are still many unknowns out there."

General Myers said coalition forces will secure Iraqi oil fields in the southern part of the country.

He also announced that troops have captured three Iraqi boats that were carrying mines, a potential threat to coalition warships.